An existing optical modulation system generally includes a driver and a modulator. Traveling-wave electrode modulators have become widely used because of their higher light extinction ratio and ease of integration. Traveling-wave electrode modulators are categorized as single-electrode driven and dual-electrode driven on the basis of the driving mode, and as serial push-pull structure and separate dual-arm structure on the basis of the optical waveguide configuration. In general, as illustrated in FIG. 1, a traveling-wave electrode modulation system 100 primarily includes a driver 20 and a traveling-wave electrode modulator 10. A diagram illustrating a cross section of the traveling-wave electrode modulator 10 is shown in FIG. 2.
The principle of operation of the traveling-wave electrode modulation system 100 is as follows. The driver 20 is connected to the traveling-wave electrode modulator 10 by means of bonded leads. An optical waveguide 130 is placed in the electric field of a traveling-wave electrode 120. A high-speed digital signal output from the driver 20 reaches the traveling-wave electrode modulator 10 and propagates along the traveling-wave electrode 120. A light wave propagates in the optical waveguide 130. A change in the electric field produced by the high-speed digital signal in the traveling-wave electrode 120 causes a change to the effective refractive index of the optical waveguide 130. Therefore, when the high-speed digital signal propagates in the traveling-wave electrode 120, the electric field of the high-speed digital signal causes a change to the refractive index of the optical waveguide 130, thereby causing a change to the phase of the light wave and causing the light wave to carry the digital signal information. Light wave interference occurs in a Mach-Zehnder interferometer at a back end, thereby completing the modulation.
During actual use, the entire traveling-wave electrode modulator chip generally is a complete chip with four, eight, or even more channels. The more the channels, the smaller the spacings between the channels, resulting in crosstalk between the channels on the chip. FIG. 3 is a diagram illustrating the electromagnetic field radiation inside a traveling-wave electrode modulator during use. As shown in FIG. 3, an optical modulator is installed on a heat sink, i.e., a heat sink pad 30 is disposed below a bottom substrate layer 110 of the chip. The heat sink pad 30 is typically a metal pad and, at the same time, functions as a metal ground layer. The electromagnetic field 150 of a signal electrode 121 might radiate into free space. Such radiation causes the problem of electromagnetic radiation. The signal electrode 121 is disposed between ground electrodes 122. A part of the electromagnetic field 150 might also couple to an adjacent channel to cause crosstalk. The crosstalk produces a noise in the signal, eventually affecting the bit error rate of a link. Moreover, a common mode voltage output from the driver 20 might cause relatively high electromagnetic radiation from the traveling-wave electrode at the end closer to the traveling-wave electrode modulator chip, causing failure of module authentication and other problems.